Dispensing System with Remotely Mounted Metering Device

ABSTRACT

A system is disclosed for dispensing a reactant into an exhaust stream. The system dispenses a mixture of reactant and pressurized air into the exhaust stream. This system includes a mixing manifold that mounts to an exhaust pipe that carries the exhaust stream. The system also includes a metering device remotely mounted from the mixing manifold.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/942,358, filed Jun. 6, 2007, which application is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to systems for dispensing a reactant into a diesel engine exhaust system.

BACKGROUND

Vehicles equipped with diesel engines may include exhaust systems that have diesel particulate filters for removing particulate matter from the exhaust stream. With use, soot or other carbon-based particulate matter accumulates on the diesel particulate filters. As particulate matter accumulates on the diesel particulate filters, the restriction of the filters increases causing the buildup of undesirable back pressure in the exhaust systems. High back pressures decrease engine efficiency. Therefore, to prevent diesel particulate filters from becoming excessively loaded, diesel particulate filters should be regularly regenerated by burning off (i.e., oxidizing) the particulates that accumulate on the filters. To initiate regeneration, some prior art systems inject a hydrocarbon based fuel into the exhaust stream at a location upstream from the diesel particulate filter. The system disclosed at PCT application PCT US04/18536, filed Jun. 10, 2004, entitled Method of Dispensing Fuel into Transient Flow of an Exhaust System, that is hereby incorporated by reference in its entirety, includes a catalytic converter positioned upstream from a diesel particulate filter. In this system, fuel is injected into the exhaust stream at a location upstream from the catalytic converter. The injected fuel is combusted at the catalytic converter to generate heat for regenerating the diesel particulate filter. In other systems, fuel is injected into the exhaust stream immediately upstream from the diesel particulate filter such that combustion of the fuel at the diesel particulate filter provides heat for regenerating the diesel particulate filter.

In addition to particulate filters for removing particulate matter, exhaust systems can be equipped with structures for removing other undesirable emissions such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). Catalytic converters are typically used to remove CO and HC. NOx can be removed by structures such as lean NOx catalysts, selective catalytic reduction (SCR) catalysts and lean NOx traps.

Lean NOx catalysts are catalysts capable of converting NOx to nitrogen and oxygen in an oxygen rich environment with the assistance of low levels of hydrocarbons. For diesel engines, hydrocarbon emissions are too low to provide adequate NOx conversion, thus hydrocarbons are required to be injected into the exhaust stream upstream of the lean NOx catalysts. SCR's are also capable of converting NOx to nitrogen and oxygen. However, in contrast to using HC's for conversion, SCR's use reductants such as urea or ammonia that are injected into the exhaust stream upstream of the SCR's. NOx traps use a material such as barium oxide to absorb NOx during lean bum operating conditions. During fuel rich operations, the NOx is desorbed and converted to nitrogen and oxygen by catalysts (e.g., precious metals) within the traps.

What is needed is an improved system for dispensing fuel, ammonia, urea or other reactants into the exhaust stream of a diesel engine.

SUMMARY

The present disclosure relates to a system for delivering a reactant into the exhaust stream of a diesel engine. A reactant dosing system dispenses a mixture of reactant and pressurized air into the exhaust stream. This system includes a mixing manifold that mounts to an exhaust pipe that carries the exhaust stream. The system also includes a metering device remotely mounted from the mixing manifold.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a dosing system having features in accordance with the principles of the present disclosure;

FIG. 2 is a schematic view showing the dosing system of FIG. 1 used to meter fuel into the exhaust stream of a diesel engine;

FIG. 3 is an exploded, perspective view of a manifold assembly having features that are examples of inventive aspects in accordance with the principles of the present disclosure;

FIG. 4 is a front view of the manifold assembly of FIG. 3;

FIG. 5 is a top view of the manifold assembly of FIG. 3;

FIG. 6 is a cross-sectional view taken along section line 6-6 of FIG. 5;

FIG. 7 is a perspective view of a manifold block used in the manifold assembly of FIG. 3;

FIG. 8 is a partially cut-away front view of the manifold block of FIG. 7;

FIG. 9 is a bottom view of the manifold block of FIG. 7;

FIG. 10 is a partially cut-away side view of the manifold block of FIG. 7;

FIG. 11 is a top view of the manifold block of FIG. 7;

FIG. 12 is a cross-sectional view taken along section line 12-12 of FIG. 8;

FIG. 13 is a cross-sectional view taken along section line 13-13 of FIG. 8;

FIG. 13A is a detailed view of a portion of FIG. 13;

FIG. 14 is a cross-sectional view taken along section line 14-14 of FIG. 8;

FIG. 15 is a perspective view of a dispensing tube that is part of the manifold assembly of FIG. 3;

FIG. 16 is a top end view of the dispensing tube of FIG. 15;

FIG. 17 is a cross-sectional view taken along section line 17-17 of FIG. 16;

FIG. 18 is a bottom view of the dispensing tube of FIG. 15;

FIG. 19 is a cross-sectional view taken along section line 19-19 of FIG. 16;

FIG. 19A is an enlarged view of a lower portion of FIG. 19;

FIG. 19B is an enlarged view of an upper portion of FIG. 19;

FIG. 20 is an end view an insert that is part of the manifold assembly of FIG. 3;

FIG. 21 is a cross-sectional view taken along section line 21-21 of FIG. 20;

FIG. 22 is an end view of a nut used to retain the dispensing tube of FIG. 15 within the manifold block of FIG. 7;

FIG. 23 is a cross-sectional view taken along section line 23-23 of FIG. 22;

FIG. 24 is a plan view of a gasket that is part of the manifold assembly of FIG. 3;

FIG. 25 is a side view of the gasket of FIG. 24;

FIG. 26 is an end view of a check valve that is incorporated into the manifold block of FIG. 7;

FIG. 27 is a partially schematic side view of the check valve of FIG. 26;

FIG. 28 is an end view of a fitting used to connect a fuel line to the manifold block of FIG. 7;

FIG. 29 is a side view of the fitting of FIG. 28;

FIG. 30 is an end view of a fitting representative of fittings that can be used at the air inlet, the cooling fluid inlet and the cooling fluid outlet of the manifold block of FIG. 7; and

FIG. 31 is a side view of the fitting of FIG. 30.

DETAILED DESCRIPTION

FIG. 1 illustrates a dosing system 20 having features that are examples of inventive aspects in accordance with the principles of the present disclosure. The dosing system 20 includes a fuel metering device 22, an air assist control unit 24, a mixing manifold 26 and an electronic control unit 28. The fuel metering device 22 and the air assist control unit 24 respectively provide fuel and air to the mixing manifold 26. At the mixing manifold 26, the fuel and air are mixed and then dispensed (e.g., sprayed) from a dispensing tube 30 that projects outwardly from the mixing manifold 26. The fuel metering device 22 is mounted remotely from the mixing manifold 26 and is connected in fluid communication with the mixing manifold 26 by a fuel line 32 (e.g., a conduit such as a pipe, tube or hose). A fuel line check valve 34 is positioned at the mixing manifold 26. The check valve 34 ensures that the fuel line 32 remains completely full of fuel even when the fuel metering device 22 is not dispensing fuel. In this way, when the fuel metering device 22 begins to dispense fuel, the check valve opens and fuel is provided immediately to the mixing manifold 26 without any significant time delay. The mixing manifold 26 also includes a cooling arrangement to prevent the check valve 34 from overheating when the dosing system 20 is used for high temperature applications. The electronic control unit 28 controls the operation of the fuel metering device 22 and the air assist control unit 24.

FIG. 2 shows an example application in which the dosing system 20 can be used. The application includes a diesel engine 36 (e.g., a diesel engine used for a vehicle such as a truck). An air intake pipe 38 provides intake air to the diesel engine 36. An exhaust pipe 40 carries diesel exhaust away from the diesel engine 36. A turbo charger 42 compresses the intake air provided to the diesel engine 36. The turbo charger 42 includes a turbine 44 located in the exhaust pipe 40 and a compressor 46 located in the air intake pipe 38. An exhaust treatment arrangement 48 is provided in the exhaust pipe 40 at a location downstream from the turbine 44. In one embodiment, the exhaust treatment arrangement 48 can include a catalytic converter positioned upstream from a diesel particulate filter. For such an embodiment, the dosing system 20 can be used to provide fuel that is combusted at the catalytic converter to provide heat for regenerating the diesel particulate filter. As disclosed at PCT application PCT US04/18536, the electronic control unit can control the amount of fuel dispensed to provide controlled regeneration of the diesel particulate filter. PCT application PCT US04/18536 also discloses example configurations for the catalytic converter and the diesel particulate filter.

Referring still to FIG. 2, the dosing system 20 is used to dispense fuel into the exhaust pipe 40 at a location upstream from the exhaust treatment arrangement 48. As shown in FIG. 2, the mixing manifold 26 mounts to the exhaust pipe 40 at a location immediately downstream from the turbo charger turbine 44. In one embodiment, the mixing manifold 26 is within two feet of the turbine 44. The fuel metering device 22, the air assist control unit 24, and the electronic control unit 28 are all remotely mounted from the mixing manifold 26. In one embodiment, the fuel metering device 22, the air assist control unit 24 and the electronic control unit 28 can be remotely mounted from the mixing manifold 26 (e.g., at other locations beneath the hood of the vehicle). During operation of the diesel engine 36, the exhaust stream in the exhaust pipe 40 at a location immediately downstream from the turbine 44 can reach high temperatures (e.g., greater than 500 degrees Celsius). Since the mixing manifold 26 is mounted to the exhaust pipe 40, it can be exposed to high temperatures. To prevent the mixing manifold 26 and its various components from being damaged by heat, the mixing manifold 26 is preferably equipped with a cooling arrangement. In one embodiment, the mixing manifold 26 defines a cooling passage through which a liquid for cooling the mixing manifold 26 can be pumped. For example, the cooling passage can be placed in fluid communication with a liquid cooling circuit 27 of the engine by cooling fluid supply and return lines 81, 83 such that a cooling liquid (e.g., a water-based cooling liquid) can be pumped through the cooling passage of the mixing manifold 26. In other embodiments, other types of cooling fluids (e.g., fuel) can be pumped through the cooling passage.

The fuel metering device 22 is in fluid communication with a source of fuel such as a fuel circuit of the diesel engine 36. Pressure for driving the fuel in the fuel circuit can be provided by a fuel pump 37 that provides fuel to the diesel engine 36. It will be appreciated that the fuel metering device 22 can have any number of different configurations. In one embodiment, the fuel metering device 22 can include a fuel injector having a metering valve that opens to provide fuel to the mixing manifold 26 and closes to stop the flow of fuel to the mixing manifold 26. This type of fuel injector typically cycles the metering valve on and off with the amount of fuel being supplied to the mixing manifold 26 being controlled by the duty cycle of the metering valve (i.e., the duration that the valve is cycled on and off). In an alternative embodiment, the fuel metering device 22 can include a spool valve that controls the fuel provided to the mixing manifold 26. The spool valve can be moved to a closed position in which fuel is not directed to the fuel line 32 and instead is directed to a fuel tank 39 of the vehicle. The spool valve is also capable of proportionately controlling the fuel flow rate provided to the mixing manifold 26 dependent upon the linear position of the spool valve. The electronic control unit 28 interfaces with the fuel metering device 22 to turn the fuel metering device 22 off and to control the flow rate of fuel provided to the mixing manifold 26 through the fuel line 32.

In a preferred embodiment, the fuel metering device 22 is remotely mounted with respect to the mixing manifold 26. For example, the fuel metering device 22 can be mounted to the engine 36 adjacent a cool side of the engine. By mounting the fuel metering device 22 to the cool side of the engine, the fuel metering device is not exposed to intense heat that can cause metering valve damage. The less severe operating conditions allow a wider variety fuel metering devices to be used. Moreover, the lower temperatures reduce possible safety concerns relating to fuel leakage.

Referring back to FIG. 1, the air assist control unit 24 includes an air manifold 50 having an air inlet 52 and an air outlet 54. The air inlet 52 is in fluid communication with a source of compressed air 53 (e.g., the compressed air tank of the truck). The air outlet 54 is connected in fluid communication with the mixing manifold 26. Preferably, the air assist control unit 24 is remotely mounted with respect to the mixing manifold 26 and the air outlet 54 is connected to the mixing manifold 26 by an air line 56 (e.g., a tube, pipe, hose or other conduit). The air assist control unit 24 also includes a number of additional components mounted to the air manifold 50. For example, an air filter 58 is mounted to the air manifold 50 for filtering the compressed air provided from the source of compressed air 53. Also, a solenoid valve 60 is mounted to the air manifold 50 for opening and closing fluid communication between the air inlet 52 and the air outlet 54. The open or closed state of the solenoid valve 60 is controlled by the electronic control unit 28. The air assist control unit 24 further includes a pressure transducer 62 mounted to the air manifold 50 for measuring the pressure of the compressed air provided to the mixing manifold 26. Pressure readings taken by the transducer 26 are provided to the electronic control unit 28.

FIGS. 3-14 show various views of the mixing manifold 26. As best shown at FIG. 3, the mixing manifold 26 includes a generally rectangular manifold block 70. In one embodiment, the manifold block 70 can be constructed of a metal material such as stainless steel. A plurality of holes can be drilled into the block 70 to define structures such as fluid passages, a mixing chamber, and fastener receiving openings. As shown at FIG. 3, the manifold block 70 includes a first side 72, a second side 74 positioned opposite from the first side 72, and a third side 76 that extends from the first side 72 to the second side 74. The dispensing tube 30 projects outwardly from the first side 72 of the manifold block 70. The fuel line 32 connects to the manifold block 70 at a fuel inlet 78 located at the second side 74 of the manifold block 70. The air line 56 connects to the manifold block 70 at an air inlet 80 located at the third side 76 of the manifold block 70. The coolant supply line 81 connects to the manifold block 70 at a coolant inlet 82 located at the third side 76 of the manifold block 70. The coolant return line 83 connects to the manifold block 70 at a coolant outlet 84 located at the third side 76 of the manifold block 70.

Referring to FIGS. 3, 5, 6 and 14, the manifold block 70 defines three fastener openings 84 that extend through the manifold block 70 from the first side 72 to the second side 74. The fastener openings 84 are adapted to receive fasteners such as bolts 90 (see FIG. 2) used to secure the manifold block 70 to the exhaust pipe 40. As shown schematically in FIG. 2, a mounting plate base 86 is secured (e.g., welded) to the exhaust pipe 40. The mounting base 86 defines three tapped openings 88 arranged to align with the fastener openings 84 of the manifold block 70. By aligning the fastener openings 84 with the tapped openings 88, bolts 90 can be inserted through the fastener openings 84 and threaded into the tapped openings 88 to secure the manifold block 70 to the mounting base 86. A gasket layer 92 can be mounted between the mounting base 86 and the first side 72 of the manifold block 70. As shown at FIGS. 24 and 25, the gasket layer 92 defines openings 94 for allowing the bolts 90 to pass through the gasket layer 92 and an opening 96 for allowing the dispensing tube 30 to pass through the gasket layer 92. The gasket layer 92 provides a seal between the mounting base 86 and the manifold block 70 to prevent exhaust from leaking from the exhaust pipe 40 at the location where the dispensing tube 30 enters the exhaust pipe 40.

Referring to FIGS. 15-19, the dispensing tube 30 is elongated along an axis 100 and includes a first end 102 positioned opposite from a second end 104. A central passage 106 extends through the dispensing tube 30 along the axis 100. The passage 106 has a chamfered portion 108 located adjacent the first end 102 of the dispensing tube 30. A dispensing orifice 110 extends from the central passage 106 through a side wall 111 of the dispensing tube 30 at a location adjacent the second end 104 of the dispensing tube 30. In certain embodiments, the dispensing orifice 110 has a diameter of less than about 0.11 inches. In other embodiments, the dispensing orifice 110 has a diameter of less than about 0.075 inches. In further embodiments, the dispensing orifice 110 has a diameter in the range of 0.04 to 0.06 inches. Of course, other sized orifices could be used as well. The side wall 111 has an outer surface 112 that is angled relative to the central axis 100. The dispensing orifice 110 preferably has an axis 114 that is generally perpendicular to the outer surface 112 and obliquely angled relative to the axis 100. The dispensing tube 30 also includes a retention flange 116 located at the first end 102 of the dispensing tube 30. In other embodiments, the dispensing tube 30 may be eliminated and the air/fuel mixture can be dispensed through an outlet defined by the manifold block or may be dispensed through another type/configuration of dispensing tube, nozzle or sprayer.

Referring to FIG. 3, the dispensing tube 30 is part of a dispensing tube assembly that also includes a washer 120, an insert piece 122 (see FIGS. 20 and 21) and a retention nut 124 (see FIGS. 22 and 23). The dispensing tube assembly mounts within a mixed fuel/air passage 126 (see FIGS. 6, 13 and 13A) that extends into the first side 72 of the manifold block 70. The mixed fuel/air passage 126 includes a mixing chamber region 126 a, a component-receiving region 126 b for receiving the inlet piece 122 and the washer 120, and an internally threaded region 126 c configured to receive the retention nut 124. To assemble the dispensing tube assembly within the manifold block 70, the inlet piece 122 and the washer 120 are first inserted within the component-receiving region 126 b of the mixed fuel/air passage 126 with the inset piece 122 seated against a shoulder 127 provided between the mixing chamber region 126 a and the component-receiving region 126 b. Thereafter, the first end 102 of the dispensing tube 30 is inserted into the mixed fuel/air passage 126 and brought into contact with the washer 120. Next, the retention nut 124 is inserted over the second end 104 of the dispensing tube 30 and is threaded into the internally threaded region 126 c of the mixed fuel/air passage 126. As the retention nut 124 is tightened, the retention nut 124 engages the retention flange 116 of the dispensing tube 30 such that the insert piece 122 is compressed against the shoulder 127 and the washer 120 is compressed between the insert piece 122 and the retention flange 116.

As best shown at FIGS. 20 and 21, the insert piece 122 has a cylindrical outer shape having a first end 130 positioned opposite from a second end 132. A tapered opening 133 (e.g., a truncated conical opening) extends through the insert piece 122 from the first end 130 to the second end 132. When the insert piece 122 is assembled within the passage 126, the first end 130 faces toward the mixing chamber region 126 a of the passage 126 and the second end 132 engages the washer 120 and aligns with the chamfered portion 108 of the dispensing tube passage 106.

Referring to FIGS. 6 and 13, the fuel inlet 78 provides access to a fuel passage 140 that extends from the second side 74 of the manifold block 70 to the mixing chamber 126 b. A check valve receptacle region 140 a of the fuel passage 140 is sized to receive the check valve 34. An internally threaded region 140 b of the fuel passage 140 is configured to receive a first threaded portion 142 of a fuel inlet fitting 144 (see FIGS. 28 and 29). A countersunk region 140 c of the fuel passage 140 is configured to receive a washer 146. The fuel inlet fitting 144 also includes a second threaded portion 143 to which a threaded connector provided on the fuel line 32 can be connected. The fuel inlet fitting 144 also includes a wrench flat portion 145 for use in tightening the first threaded portion 142 within the internally threaded region 140 b of the fuel passage 140. The fuel passage 140 also includes an end region 140 d that provides fluid communication with the mixing chamber 126 b.

As shown in FIGS. 6, 26, and 27, the check valve 34 includes a shuttle member 150 that moves within a check valve housing 151 to open and close fluid communication between the fuel line 32 and the mixing chamber 126 b. A sealing member 153 (e.g., an o-ring seal) surrounds the valve housing 151 and forms a seal between the housing 151 and the check valve receptacle region 140 a of the fuel passage 140. An elastomeric valve seat 152 is provided within the check valve 34. A spring 154 biases the shuttle member 150 against the valve seat 152. When the fuel metering device 22 is open so as to direct fuel into the fuel line 32, the shuttle member 150 is pushed away from the valve seat 152 overcoming the bias of the spring 154 to allow fuel to pass through the check valve 34 to an end region 140 d of the fuel passage 140. The end region 140 d of the fuel passage 140 is in fluid communication with the mixing chamber 126 b of the mixed fuel/air passage 126.

The air inlet 80 provides access to an air passage 160 that extends from the third side 76 of the manifold block 70 to the mixing chamber 126 b. The air passage 160 includes a first straight segment 162, a second straight segment 164, and a third straight segment 166. As shown at FIG. 10, the first segment 162 includes a counter sunk region 162 a for receiving a washer 168. The first segment 162 also includes an internally threaded region 162 b for receiving a first threaded portion 170 of a fitting 172 (see FIGS. 30 and 31). The fitting 172 also includes a second threaded portion 174 to which a threaded connector provided at the end of the air line 56 can be connected. The fitting 172 can include wrench flats 176 for use in tightening the fitting 172 within the internally threaded region 162 b. The first segment 162 further includes an end region 162 c that extends from the internally threaded region 162 b to the second straight segment 164 of the air passage 160.

As shown at FIGS. 8 and 10, the second straight segment 164 of the air passage 160 extends from the second side 174 of the manifold block 70, through the end region 162 c of the fiber straight segment 162, to the third straight segment 166. A plug 180 is provided in the second straight segment 164 adjacent the second side 74 of the manifold block 70 to close the end of the segment 164.

As shown at FIGS. 8, 10 and 13, the third straight segment 166 of the air passage 160 extends from a fourth side 77 of the manifold block 70, through the second straight segment 164 and into the mixing chamber 126 b. A plug 182 is provided within the third straight segment 166 adjacent the fourth side 77 to close the end of the segment 166.

Referring to FIG. 12, a generally U-shaped coolant passage 200 extends through the manifold block 70 from the coolant inlet 82, around the mixed air/fuel passage 126 to the coolant outlet 84. The coolant passage 200 is formed by a first straight segment 202, a second straight segment 204 and a third straight segment 206. The first segment 202 extends from the coolant inlet 82 to the second segment 204. The second segment 204 extends from the fourth side 77 of the manifold block 70 and intersects both the first segment 202 and the third segment 206. A plug 208 is inserted into the second segment 204 adjacent the fourth side 77 to close the end of the second segment 204. The third segment 206 extends from the coolant outlet 84 at the third side 76 of the manifold block 70 to the second segment 204. Adjacent the third side 76 of the manifold block 70, the first and third segments 202, 206 define internally threaded regions 210 into which fittings 212 can be threaded. The fittings 212 can have a similar configuration to the fitting 172 of FIGS. 30 and 31.

In use of the system, when the diesel engine is started, cooling fluid (e.g., a water-based cooling liquid) is circulated from the engine water circuit through the cooling passage 200 of the manifold block 70. The circulation of cooling fluid assists in maintaining the manifold block 70 at a temperature where elastomeric components of the check valve 34 are not damaged. This is particularly significant for applications where the manifold block 70 is mounted to an exhaust pipe in close proximity to the diesel engine. When it is desired to supply fuel to the exhaust stream, the electronic control unit 28 actuates the air assist control unit 24 and the fuel metering device 22. When the fuel metering device 22 is actuated to dispense a desired amount of fuel, the check valve 34 is pushed open thereby allowing fuel to flow from the fuel line 32 to pass through the fuel passage 140 and into the mixing chamber 126 b. The fuel entering the mixing chamber 126 b mixes with air from the air line 56 that is directed into the mixing chamber 126 b via the air passage 160. The mixed air and fuel flow from the mixing chamber 126 b, through the insert piece 122 and into the passage 106 of the dispensing tube 30. From the passage 106, the mixture of fuel and air is dispensed through the dispensing orifice 110 into the exhaust stream.

In the above embodiments, fuel (e.g., a hydrocarbon based fuel) is injected into the exhaust stream to raise exhaust temperatures to a target temperature suitable for regenerating a diesel particulate filter. In other embodiments, the dosing systems disclosed herein can be used to inject a reactant into an exhaust stream for other purposes, such as to provide hydrocarbons to promote the conversion of NOx at a lean NOx catalyst or to provide hydrocarbons for regenerating NOx traps. In yet other embodiments, the metering system disclosed herein can be used to dispense a reductant, such as ammonia or urea, into an exhaust stream for use with a selective catalytic reduction system for reducing NOx emissions. A variety of control models or strategies can be used by the electronic controller to control metering rates for these alternative systems. 

1. A system for dispensing a reactant into an exhaust stream, the system comprising: a manifold defining a mixing chamber, an air passage that extends to the mixing chamber, a reactant passage that extends to the mixing chamber, and a cooling passage for circulating a liquid cooling fluid through the manifold; a mixed air/reactant outlet in fluid communication with the mixing chamber; and a metering device for controlling the flow of reactant to the reactant passage, the metering device being remotely mounted from the manifold and connected to the reactant passage by a reactant line.
 2. The system of claim 1, further comprising a check valve positioned at the reactant passage.
 3. The system of claim 2, wherein the check valve ensures that the reactant line remains full of reactant even when the metering device is not dispensing reactant.
 4. The system of claim 1, wherein the metering device includes a valve that is opened and closed based on input from an electronic control unit.
 5. The system of claim 1, wherein the metering device includes a fuel injector.
 6. The system of claim 1, wherein the metering device includes a spool valve.
 7. The system of claim 1, wherein the mixed air/reactant outlet includes a dispensing tube having an end that mounts within a mixed reactant/air passage of the manifold, and wherein the cooling passage is generally u-shaped and loops around the mixed reactant/air passage.
 8. The system of claim 1, further comprising a dispensing tube that projects outwardly from the manifold and defines the mixed air/reactant outlet.
 9. The system of claim 8, wherein the dispensing tube defines a dispensing orifice through a side wall of the dispensing tube.
 10. The system of claim 9, wherein the dispensing orifice has a diameter less than 0.11 inches.
 11. The system of claim 10, wherein the dispensing orifice has a diameter in the range of 0.04 to 0.06 inches.
 12. The system of claim 9, wherein the side wall includes an outer surface aligned at an oblique angle relative to a central axis of the dispensing tube.
 13. The system of claim 12, wherein the dispensing orifice defines a central axis that is generally perpendicular to the outer surface of the side wall.
 14. The system of claim 7, wherein the manifold includes a generally rectangular manifold block having a first side positioned opposite from a second side, and a third side that extends from the first side to the second side, wherein the dispensing tube projects outwardly from the first side of the manifold block, wherein a reactant inlet for accessing the reactant passage is located at the second side of the manifold block, wherein an air inlet for accessing the air passage is defined at the third side of the block, wherein a cooling fluid inlet for accessing the cooling passage is defined at the third side of the block, and wherein a cooling fluid outlet for accessing the cooling passage is defined at the third side.
 15. A system for dispensing a reactant into an exhaust stream, the system comprising: a manifold defining a mixing chamber, an air passage that extends to the mixing chamber, a reactant passage that extends to the mixing chamber; a mixed air/reactant outlet in fluid communication with the mixing chamber; a metering device for controlling the flow of reactant to the reactant passage, the metering device being remotely mounted from the manifold and connected to the reactant passage by a reactant line; and a check valve positioned at the reactant passage, wherein the check valve ensures that the reactant line remains full of reactant even when the metering device is not dispensing reactant. 